Stent

ABSTRACT

A bioabsorable stent is disclosed. The stent is made of a bioabsorable material and has an elongated body having a proximate end, a distal end, and at least one open channel formed on the exterior surface of the elongated body to provide fluid communication between the proximal end and the distal end. Also disclosed is a bioabsorable stent having an elongated center rod having a proximate end and a distal end and a plurality of leaflets extending outward from the center rod and forming channels between two neighboring leaflets to provide fluid communication between the proximal end and the distal end.

This application is a continuation application of the U.S. patentapplication Ser. No. 12/417,122, filed Apr. 2, 2009, which claimspriority to U.S. Patent Application Ser. No. 61/129,203, filed Jun. 11,2008. The entirety of all of the aforementioned applications isincorporated herein by reference.

FIELD

The present invention generally relates to medical devices and, inparticular, to a stent with one or more open channels formed on itsexterior surface.

BACKGROUND

In medical terms, a stent is a man-made “tube” inserted into a naturalpassage or conduit in the body to prevent, or counteract, adisease-induced, localized flow constriction. The term may also refer toa tube used to temporarily hold such a natural conduit open to allowaccess for surgery. Stents include vascular and non-vascular stents.Vascular stents are designed for applications in the vascular system,such as arteries and veins. Non-vascular stents are used in other bodylumens such as biliary, colorectal, esophageal, ureteral and urethraltract, and upper airway

Stents are available in permanent and temporary varieties. Stentduration is heavily influenced by the construction material. Forexample, metal stents typically have a much longer use life than plasticstents. The stent body typically has a central lumen that allows bloodor other body fluid to flow through the stent. A common problem with thecurrent stents is that they routinely migrate and clog, thus requiringadditional procedures for extraction and/or replacement. There exists aneed for improved stents that are easy to make and safe to use.

SUMMARY

A bioabsorable stent is disclosed. The stent includes an elongated stentbody having a proximate end, a distal end, and at least one open channelformed on the exterior surface of the elongated stent body to providefluid communication between the proximal end and the distal end. Theelongated stent body comprises a bioabsorable material.

In a related embodiment, the open channel is a sinusoidal channel on theexterior surface of the elongated stent body.

In another related embodiment, the sinusoidal channel has aconcentrically consistent pitch.

In another related embodiment, the sinusoidal channel has a concentricpitch that changes in its length over the device.

In another related embodiment, the elongated stent body comprises aplurality of channels on the exterior surface.

In another related embodiment, the distal end and the proximate end ofthe channels have different diameters.

In another related embodiment, the distal end and the proximate end ofthe stent have different diameters.

In another related embodiment, the open channel has different depthsfrom one end of the stent to the other or intermittently at varyingpoints through the length of the stent.

In another embodiment the open channel has varying diameters.

In another embodiment, the ends of the elongate stent body havedifferent shapes.

In another related embodiment, the elongated stent body has a sinusoidalshape.

In another related embodiment, the elongated stent body further includesa center lumen.

In another related embodiment, the sinusoidal pitch may span or extendover the entire length of an interior surface of the stent body.

In another related embodiment, the sinusoidal pitch may span or extendover a portion of an interior surface of the stent body or only aportion of an exterior surface of the stent body.

In another related embodiment, the sinusoidal pitch may span or extendover the interior surface and exterior surface of the device throughoutits wall thickness or over a portion of its wall thickness or over aportion of the interior surface and exterior surface of the stent body.

In another related embodiment, the elongated stent body further includesan anchoring device.

In another related embodiment, the elongated stent body further includesa biological agent.

In another related embodiment, the biological agent is selected from thegroup consisting of chemotherapeutic agents, antimicrobial agents andgene transfer agents.

In another related embodiment, the open channel is formed bycompressible channel walls that can be compressed against each other ina compressed state to reduce the diameter of the stent.

Also disclosed is a stent having an elongated stent body with aproximate end, a distal end, and at least one sinusoidal channel ortrack on an exterior surface of the body to provide fluid communicationbetween the proximal end and the distal end. The distal end and theproximate end of the stent have different diameters.

In a related embodiment, the elongated stent body is made of abioabsorable material.

In another related embodiment, the elongated stent body further containsa center lumen.

In another related embodiment, the sinusoidal channel is formed betweentwo collapsible channel walls.

Also disclosed is a stent that includes an elongated center rod having aproximate end and a distal end, and a plurality of leaflets extendingoutward from the center rod and forming channels between two neighboringleaflets to provide fluid communication between said proximal end andsaid distal end. The center rod and the leaflets are made of abioabsorable material.

In a related embodiment, the plurality of leaflets can be folded toreduce the diameter of the stent.

In a related embodiment, the plurality of leaflets can be foldedpivotally over each other.

Also disclosed is a kit for stent implantation. The kit includes: astent having an elongated stent body with a proximate end, a distal end,and at least one open channel formed the exterior surface of the body toprovide fluid communication between the proximal end and the distal end;a guide wire; and a pusher tube that is movable along the guide wire.

In a related embodiment, the elongated stent body is made of abioabsorable material.

In another related embodiment, the elongated stent body of the stentfurther contains a center lumen to adopt the guide wire.

In another related embodiment, the elongated stent body is made of amixture of compounds.

In another related embodiment, the elongated stent body is made of amagnesium and chitin alloy.

In another related embodiment, the elongated stent body is made with amagnesium core coated with a chitin chitosan, N-acylchitosan hydrogelouter layer. The magnesium core may additionally include rare earthmaterials.

In another related embodiment, the elongated stent body is made of achitin and chitosan, N-acylchitosan hydrogel and magnesium alloy withraw earth elements.

Also disclosed is a method for stabilizing bone fracture. The methodincludes inserting the stent of the present invention into the canal ofa bone having a fracture.

In a related embodiment, the stent is coated with a hydrogel. Thehydrogel expands by absorbing of fluids and improves the connection andsupport of the inner wall of the bone canal.

In another related embodiment, the stent is used to attach bonefractures together.

In another embodiment, the stent is placed through the bone cortex.

In another embodiment, the stent is imbedded with barium sulphate orother metallic particles or contrast agents to allow all or a part ofthe stent to be seen under imaging.

In another embodiment, the stent is coated with a biodegradable materialto control its properties, including mechanical strength,biocompatibility, biodegradation, diffusibility, and absorptionproperties.

In another embodiment, the stent degrade in situ by hydrolyticreactions, enzymatic reactions, alkaline or pH elevations.

BRIEF DESCRIPTION OF DRAWINGS

The present invention can be better understood by reference to thefollowing drawings, wherein like references numerals represent likeelements. The drawings are merely exemplary to illustrate certainfeatures that may be used singularly or in combination with otherfeatures and the present invention should not be limited to theembodiments shown.

FIG. 1A is a diagram showing an embodiment of the stent of the presentinvention. FIG. 1B is a see-through illustration of FIG. 1A.

FIG. 2 is a diagram showing a stent with a sinusoidal shaped stent body.

FIG. 3 is a diagram showing an assembly of a stent with a guide wire anda pusher tube.

FIGS. 4A and 4B are diagrams showing two engagement mechanisms among thestent, the guide wire and the pusher tube.

FIGS. 5A and 5B show an embodiment of an expandable stent.

FIGS. 6A and 6B show another embodiment of an expandable stent.

FIGS. 7A and 7B show another embodiment of an expandable stent.

FIGS. 8A-8E show various embodiments of an expandable stent.

FIGS. 9A-9C show several embodiments of a stent with an outer frame.

FIG. 10 shows another embodiment of a stent with sinusoidal channels ofvarying pitches.

FIGS. 11A-11B shows another embodiment of a stent of the presentinvention.

FIG. 12 shows another embodiment of a stent of the present invention.

FIG. 13 shows the cross section of an embodiment of a stent of thepresent invention.

FIG. 14 shows the cross section of another embodiment of a stent of thepresent invention.

FIG. 15 shows another embodiment of a stent of the present invention.

FIG. 16 shows another embodiment of a stent of the present invention.

FIG. 17 shows another embodiment of a stent of the present invention.

FIG. 18 shows another embodiment of a stent of the present invention.

DETAILED DESCRIPTION

The practice of the present invention will employ, unless otherwiseindicated, conventional medical devices and methods within the skill ofthe art. Such techniques are explained fully in the literature. Allpublications, patents and patent applications cited herein, whethersupra or infra, are hereby incorporated by reference in their entirety.

One aspect of the present invention relates to a stent that contains anelongated stent body having a proximate end, a distal end, and at leastone open channel formed on the exterior surface of the elongated stentbody to provide fluid communication from the proximal end to the distalend of the stent.

As used herein, the term “stent” refers to a device which is implantedwithin a bodily lumen to hold open the lumen or to reinforce a smallsegment of the lumen. Stents can be used for treating obstructedvessels, biliary ducts, pancreatic ducts, ureters, or other obstructedlumens, fractured canals, bones with hollow centers and/or fordelivering various drugs through controlled release to the particularlumen of interest.

The open channel should be large enough to allow unobstructed or normalflow of various body fluids such as blood, bile or urine or otherluminal material/liquids on the outer aspect of the stent. The openchannel may have a cross section area that is of any shape or depth. Thechannel could be V shapes, U shaped, or with a rising or falling pitch,of an even depth or one that is of varying widths, depths, varying andcircumferential rotations changing at various points over the length ofthe device. The channel can be a straight channel or a spiral channel.Multiple channels may be formed on the exterior surface or the innersurface of the elongated stent body. The channel(s) may also be designedwith a geometry that would help the stent to remain in place.

The shape, length and diameter of the stent body are applicationdependent. The elongated stent body can be straight or curved or in theshape of multiply connected and angulated curves. Each type of stent isdesigned to fit within a specific part of the anatomy. Therefore, theshape, length, and diameter of stents differ by type to accommodate andsupport different sized lumens and different clinical needs. Forexample, each major stent application, such as vascular, pancreatic,ureteral, or metacarpal canal, other hollow bone structures and otherstent, requires a different diameter and shape to enable placement, toremain in place after placement, to stabilize and support the anatomy itis placed in, and to allow conformance to the normal anatomy. As usedherein, the diameter of a stent refers to the width across the shaft ofthe stent body, which is also referred to as the “major diameter.” Inone embodiment, the stent has a uniform diameter. In another embodiment,the stent has a variable diameter. In one embodiment, the diameter atthe distal end is smaller than the diameter at the proximate end. Inanother embodiment, the diameter at the proximate end is smaller thanthe diameter at the distal end. In yet another embodiment, the diametersat the distal end and the proximate end are both smaller than thediameter at the middle section of the stent.

The stent body may further include a center lumen to accommodate a guidewire. This center lumen may provide additionally flow throughput afterthe removal of guide wire.

In one embodiment, the stent is naturally formed by braiding multiplefilaments together. In another embodiment, the stent is made with acenter rod/hub/cam having one or more sinusoidal channels runningthrough the exterior surface of the center rod, similar to that of adrillbit.

The stent of the present invention can be expandable. In one embodiment,the stent is of two different diametrical dimensions due to radialdeformation of its elastic elements. Before being positioned at theplace of reconstruction, the stent is deformed/compressed/folded so asto minimize its diametrical dimension. Then the stent is placed, in thedeformed state, inside a transporting means by arranging it on a specialsetting bulb. Once the stent has been transported to the place ofreconstruction, the setting bulb is expanded so that the stent diameteris maximized. In another embodiment, the stent has a plurality offlexible or foldable channel walls or leaflets extending from the centerrod/hub/cam. The channel walls or leaflets are kept in a folded positionduring the delivery process and are released only at the treatment site.

In one embodiment, the stent is delivered to the treatment site in abody lumen with a pusher rod that pushes the stent through a bodychannel into place. The pusher rod travels over a guide wire. The pusherrod is designed in such a way to attach to the ends of the stent toassist with directing the delivery. In one embodiment, the pusher rodinterlocks with the proximate end of the stent in a male/female fashion,much the same way a wrench fits over a nut.

FIG. 1A is a diagram showing an embodiment of the stent of the presentinvention. In this embodiment, stent 100 has an elongated body 10 with aproximate end 12 and a distal end 14. Two sinusoidal channels 16 areformed on the exterior surface of the elongated body 10, extending fromthe proximate end 12 to the distal end 14 in a fashion similar to thegrooves on a drill head. The channels may have beveled edges tofacilitate fluid flow inside the channels. The channels can be ofvarying depths and lengths. The ends of the stent body can be of variousshapes including conical shape. FIG. 1B is a see-through drawing of FIG.1A. The two-channel design allows for two channels on the exteriorsurface of the stent to run in parallel from one end to the other or tocriss-cross to allow for increased fluid flow as well as the ability toincrease side branch flow of the main stented channel.

A center lumen 20 allows the stent 100 to slide into the place ofimplantation through a guide wire.

FIG. 2 shows another embodiment of the stent of the present invention.In this embodiment, stent 200 has a modified sinusoidial body shape toimprove flexibility, allow for varying flow dynamics, and facilitatecontour and wall adherence to the lumens. The multiple V shaped channels16 allow for the flow of various body fluids. The diameter of theinternal lumen 20 and the outer diameter of the stent body can bechanged based on the need for various luminal dimensions, shapes, flows,and biomechanics. The tapered tip 18 facilitates advancement of thestent inside a body lumen.

FIGS. 13 and 14 show cross-sections of V-shaped channel and channelwalls. The channels can be of varying depths and varying widths tochange the volume and speed of fluid flow. The bottom of the channel canbe rounded or tapered or formed by a direct angle.

The stent of the present invention may be implanted with procedures wellknown to a person of ordinary skill in the art. Examples of suchprocedures include, but are not limited to, standard percutaneousapproach using a guide wire, endoscopic retrogradecholangiopancreatography (ERCP) placement procedures, and otherradiographic/angiographic procedures. FIG. 3 shows an assembly of astent 200 with a guide wire 24 and a pusher tube 26. FIG. 4 showsseveral engagement mechanisms among the stent 300, the guide wire 24 andthe pusher 26. In FIG. 4A, the pusher tube has several fingers to holdthe stent 300 like a hand or clamp. In FIG. 4B, the pusher 26 interlockswith the stent 300 in a male/female fashion to ensure security ofpositioning and delivery of the stent 300. The interlacking mechanismmay involve a male to female interconnect of various shapes, sizes, ordimensions.

FIGS. 5A and 5B show an embodiment of an expandable stent 500 withcompressible channel walls 50. In a closed state (FIG. 5A), the channelwalls 50 are compressed or twisted against each other to reduce stentdiameter. Once the stent has been transported to the treatment site, thechannel walls are restored to their natural shape (FIG. 5B).

FIGS. 6A and 6B show another embodiment of an expandable stent 600 withfoldable leaflets 60. In an extended state, the thin leaflets 60 allowfor unobstructed flow of body fluid (FIG. 6A). In one embodiment, theleaflets 60 are contoured and aligned in a way to increase the flowspeed of the body fluid or to provide minimal drag. The impedance of theflow volumes and the velocity can be modulated by changing the anglesand contour of the leaflets. Additionally the interconnecting supportscan be thicker at the cam to provide different levels of stability andrigidity for the bracing arms 62, which help support the structure theyare placed in. The bracing arms 62 can be connected at anywhere alongtheir diameter and the change in connection points will have an impact Ithe rigidity of the support of the lumen, the ability of the device toflex with the normal body movement of the lumen and will change theminimal diameter the device can be collapsed in. The stent 600 mayfurther contain a center lumen 20.

As shown in FIG. 6B, the leaflets 60 may be rotated pivotally (e.g.,clockwise) to collapse into each other to reduce the size of the stentto facilitate implantation. Once in place, the stent may be rotated inan opposite direction (e.g., counter clockwise) to restore to itsextended state. The tip of the stent 600 can be titled or coned orshaped into various configurations to allow for access to different bodylumens. The opened leaflets 60 further have the benefit to preventmigration of the stent 600.

FIGS. 7A and 7B show another embodiment. In this embodiment, theexpandable stent 700 has closed connections around each alternatingleaflet 70 to allow for changes in flexibility, radial force,compression resistance, and absorption. The leaflets 70 have asinusoidal pattern and can be thicker at the attachment to inner cam 72to allow for variations of rigidity. The outer cam 74 prevents tissuegrowth inside the stent body and increases contact area between thestent 700 and inner wall of the body lumen. The thickness of outer cam74 is application dependent. The outer cam 74 may also be beveled. Thestent 700 may have a removal grip attached to the end of center lumen 20to allow for easy removal of the stent 700.

FIG. 7B shows another embodiment of the stent 700. In this embodiment,the leaflets 70 are connected to the cam 72 and can be compress downtowards the cam 74. The leaflets may have a hollow interior so thatfluid may flow through and around the leaflets 70.

In another embodiment, stent 800 contains propeller-like leaflets 80that are thicker at the base where they are attached to the cam or rodportion 82 of the stent 800. The leaflets 80 become thinner at the tip(FIG. 8A). The stent 800 may also have a sinusoidal shape to conform toa body lumen.

The propeller-like stent 800 may be constructed in such a way to allowunidirectional collapse of the leaflets to facilitate ease of passagethrough the working channel of an endoscope, bronchoscope, or throughsome other tubular delivery apparatus or opening by simply rotating thestent in a unidirectional manner and then reversing the technique toopen the stent once it is in place. Additionally, the tip of the stent800 may be shaped to allow for ease of collapse or insertion. FIG. 8Bshows a stent 800 in a collapsed configuration.

FIG. 8C shows another embodiment of the stent 800. In this embodiment,the leaflets 80 can be folded towards the cam or rod portion 82 of thestent body, in a manner similar to that of an umbrella. The leaflets 80can be in any shape, such as round, oval, triangle etc. and will have achange in thickness at the base where the leaflets are connected to thecam 82 to allow you to change ease or rigidity of folding the device andpassing it through and opening or channel. The unidirectional leafletsallow the device to be pushed through an opening and then pulled back tosecure it in place. In another embodiment, the leaflets can be foldedtowards the cam or rod portion of the stent body, in a manner similar tothat of an umbrella, a collapsing tree, or unidirectional ormultidirectional folding leaflets of consistent or varying shapes. FIG.8D shows the stent of FIG. 8C in a collapsed configuration.

In another embodiment, the leaflets 80 of the stent 800 can be foldedtogether by rotating along a common axis. FIGS. 8E and 8F show a stent800 in open and folded configurations, respectively. In one embodiment,the stent 800 has a diameter of 1 cm in open configuration and adiameter of 1 mm in folded configuration. Depending on flowrequirements, the channel 88 may have raps ranging from 5° to 100°. Incertain embodiments, the channel has a rap of 5°, 10°, 20°, 30°, 40°,50°, 60°, 70°, 80°, 90°, or 100°.

In another embodiment, a device has a portion of the device and stentand its leaflets collapsible so that some portion of the device (e.g.,1%) would have uni-direction leaflets and the remainder would have theopposite facing leaflets or directions such as seen on the differentblades of a saw. In yet another embodiment, the leaflets are alternatingin directions so as to prevent migration of the expanded stent.

Referring now to FIG. 9A an embodiment of stent 900 has a taperedproximal end 901 to allow ease of passage inside a body lumen, an outerframe 902 with a larger diameter to provide stiffness, and a center core903 with a smaller diameter to provide flexibility. The outer frame 902and the center core 903 can be cylindrical or cut with various contoursin the surface to change the flexibility or rigidity of the stent. InFIG. 9B, the stent 900 has an outer frame 902 that forms a coil aroundthe core 903. The stent 900 may further include a center lumen 20. InFIG. 9C, the stent 900 has sinusoidal channel 904 formed on the surfaceof outer frame 902. The channel 904 may have variable depth. The centercore 903 may have various shapes and sizes to adjust the flexibility,stability and rigidity of the stent 900.

In one embodiment, the stent 900 is inserted into the canal of a bonehaving a fracture. In another embodiment, the stent 900 is coated with ahydrogel. The hydrogel expands by absorbing of fluids and improves theconnection and support of the inner wall of the bone canal. In anotherembodiment, the stent 900 is used to attach bone fractures together. Inanother embodiment, the stent 900 is placed through the bone cortex.

Referring now to FIG. 10, another embodiment of a stent 1000 haschannels of varying widths and depths on the exterior of the stent body.For example channel 1001 has a width that is greater than the width ofchannel 1003. The variable width and depth can be used to change theflow of fluids or friction to the lumen it is place in. Similar channelsmay also be formed on the interior side of a tubular stent. In theembodiment shown in FIG. 10, the stent 1000 has a tapered tip 1005 tofacilitate advancement of the stent inside a body lumen. The wide distalflare 1007 prevents migration and increases stability of the stent 900.The stent 1000 may have channels of shorter or longer pitches to enableincreases in fluid flow and stability. The stent 1000 may furtherinclude a center lumen for a guide wire or fluid flow.

Referring now to FIGS. 11A-11B, another embodiment of a stent 1100 has alarger proximal end 1101 with a helical surface channel 1103. The stent1100 is in the shape of a cone or a cylinder with alternating variationin the diameter of the stent body. The surface channel 1103 may haveregions 1104, 1105 and 1106 with different shapes and depth in eachregion, so as to change the flow rate, flow volume, and/or in eachregion.

FIG. 12 shows another embodiment of a stent 1200. The pitch of the stentcan change in various zones of the stent. The stent has a smallerdiameter in the proximal end 1201 and larger diameter in the distal end1203. The stent 1200 may have an opening 1205 that is big enough toadapt a wire. The stent 1200 may have a gradual increasing or decreasingpitch. In another embodiment, the pitch may change in different sectionsof the stent to better contour to the anatomy.

Other embodiments of stents of the present invention are shown in FIGS.15-18.

FIG. 15 shows an embodiment of a stent 1500 with a conical tip 1501 toallow for ease of access into the area it will be placed, a flareddistal end 1503 for anchoring or prevention of migration into a lumen,out of a lumen, or within a lumen. The flares 1505 can be unidirectionalor bi directional.

FIG. 16 shows an embodiment of a stent 1600 with a conical end 1601 anda swollen middle section 1603. The stent 1600 may be made from anelastomer. In one embodiment, the elastomer may expands more in a areain the middle, the end, or in multiple locations of the stent body toincrease fluid flow by providing larger and deeper channels in thestent. In another embodiment, the end of the stent 1600 has an antimigration mechanism that will expand to keep the stent in place. Antimigration device at the distal end 1605 of the stent can be locatedanywhere along the length of the stent access.

FIG. 17 shows another embodiment of a stent 1700 with leaflets 1701 toform channels 1703. In this embodiment, the stent 1700 has a tapered end1705 to allow for ease of entry. The rotation of the sinusoidal channels1703 may be changed to adjust fluid flow, collapse ability, etc. Theleaflets attached to the cam 1707 can be folded over to allow thediameter of the stent 1700 to become smaller when being loaded into adeliver device or being place in a deliver tube like an endoscope. Thechannels walls can be straight, rounded, or a combination thereofdepending on the cavity or lumen where the stent is placed.

FIG. 18 shows another embodiment of a stent 1800. The stent 1800 is madein a way to allow the sinusoidal channel of the stent occur on theinside of the stent. The outside of the stent conforms to the anatomythe stent is placed in and flexibility is determined by the pitch of thesinusoidal channel. The inside of the stent forms the same sinusoidal asthe outside of the stent. In one embodiment, the stent 1800 is made insuch a way that it can be inserted in a screw in fashion.

A person or ordinary skill in the art would understand that otherfolding or interlocking may also be employed. The channel walls orleaflets can also be of varying thicknesses and lengths to provide thestent with desired rigidity, flexibility, pushability, trackability,luminal contact and/or absorption profile. For example, a stent madefrom bioabsorable material may have leaflets that are thinner at the tip(where they touch the lumen wall) and thicker at the base (where theyare attached to the cam), thus allowing for degradation from the tip tothe base. In another embodiment, the cam itself can be cut in variousways to change its diameter at different points to change thepushability and flexibility of the device.

The stent of the present invention is typically made from plastics,metals, or alloys. Notable variations exist within each type. Forexample, self-expanding metal stents are generally made from nitinol,while some balloon-expandable metal stents are made from stainlesssteel. A coating, such as polyurethane coating, may be used to preventstent material from coming into direct contact with its surroundings.The coating slows down the rate of in-growth, allowing the stent toremain in the patient with a lower potential for side effects.

The stent may also be made with a bioabsorable material. Examples ofbioabsorable materials include, but are not limited to, polylactic acidor polylactide (PLA), polyglycolic acid or polyglycolide (PGA),poly-.epsilon.-caprolactone (PCL), polyhydroxybutyrate (PHB), anco-polymers thereof.

In one embodiment, the bioabsorable material is degraded based onvarying levels of pH. For example, the material may be stable at aneutral pH but degrades at a high pH. Examples of such materialsinclude, but are not limited to chitin and chitosean. In anotherembodiment, the bioabsorable material is degradable by enzymes, such aslysozymes.

In another embodiment, the bioabsorable material may absorb moisture andexpand in situ at the treatment site. For example, the stent made ofChitin or a variable copolymer of Chitin and PLGA or Chitin andMagnesium and other raw earth minerals would swell once it comes intocontact with various body fluids. In one embodiment, the stent has apre-implantation diameter Dpre (i.e., dry diameter) of 2.8 mm and isexpandable to a post-implantation diameter Dpost, (i.e., wet diameter)of 3.3 mm after exposure to body liquid in a lumen. As used hereinafter,the “pre-implantation diameter Dpre” refers to the largest diameter of astent body before implantation and the “post-implantation diameterDpost” refers to the largest diameter of the stent body afterimplantation.

In another embodiment, the bioabsorable material is embedded with, orconfigured to carry, various agents or cells. The agents may be coupledto the outer and/or inner surfaces of stent body or integrated into thebioabsorable material itself. In one embodiment, the bioabsorable stenthas a hollow center lumen so that agents may be placed inside the lumento increase the dose release. The stent can additionally have multiplereservoirs, one inside the other, so that when the outer layer isabsorbed the next reservoir is exposed and a further release of a largerdose of the chosen agents or cells. The chosen agent or cells may alsobe mixed with the polymer for sustained release.

Examples of agents that can be embedded into or carried by a stentinclude, but are not limited to, small molecule drags, biologicals andgene transfer vectors. Examples of small molecule drugs include, but arenot limited to, sirolumus, rapamycian, and other antiproliferatingagent.

Examples of biologicals include, but are not limited to, antimicrobialagents and chemotherapeutic agents.

The term “antimicrobial agent” as used in the present invention meansantibiotics, antiseptics, disinfectants and other synthetic moieties,and combinations thereof, that are soluble in organic solvents such asalcohols, ketones, ethers, aldehydes, acetonitrile, acetic acid, formicacid, methylene chloride and chloroform. Classes of antibiotics that canpossibly be used include tetracyclines (i.e., minocycline), rifamycins(i.e., rifampin), macrolides (i.e., erythromycin), penicillins (i.e.,nafcillin), cephalosporins (i.e., cefazolin), other beta-lactamantibiotics (imipenem, aztreonam), aminoglycosides (i.e., gentamicin),chloramphenicol, sulfonamides (i.e., sulfamethoxazole), glycopeptides(i.e., vancomycm), quinolones (i.e., ciprofloxacin), fusidic acid,trimethoprim, metronidazole, clindamycin, mupirocin, polyenes (i.e.,amphotericin B), azoles (i.e., fluconazole) and beta-lactam inhibitors(i.e., sulbactam).

Examples of specific antibiotics that can be used include minocycline,rifampin, erythromycin, nafcillin, cefazolin, imipenem, aztreonam,gentamicin, sulfamethoxazole, vancomycin, ciprofloxacin, trimethoprim,metronidazole, clindamycin, teicoplanin, mupirocin, azithromycin,clarithromycin, ofloxacin, lomefloxacin, norfloxacin, nalidixic acid,sparfloxacin, pefloxacin, amifloxacin, enoxacin, fleroxacin,temafloxacin, tosufloxacin, clinafloxacin, sulbactam, clavulanic acid,amphotericin B, fluconazole, itraconazole, ketoconazole and nystatin.Other examples of antibiotics, such as those listed in U.S. Pat. No.4,642,104, herein incorporated by reference, will readily suggestthemselves to those of ordinary skill in the art. Examples ofantiseptics and disinfectants are thymol, a-terpineol,methylisothiazolone, cetylpyridinium, chloroxylenol, hexachlorophene,cationic biguanides (i.e., chlorhexidine, cyclohexidine),methylenechloride, iodine and iodophores (i.e., povidone-iodine),triclos an, furanmedical preparations (i.e., nitrofurantoin,nitrofurazone), methenamine, aldehydes (i.e., glutaraldehyde,formaldehyde) and alcohols. Other examples of antiseptics anddisinfectants will readily suggest themselves to those of ordinary skillin the art.

The stent of the present invention may also be prepared withantimicrobial agents in other ways customary in the art. For example,the stent may be made in its entirety or in part of an antimicrobialpolymer, or at least one surface of the stent may have embedded, by ionbeam assisted deposition or co-extrusion techniques, therein with atomsof an antimicrobial polymer. Other suitable examples can be found in theart, for example, U.S. Pat. No. 5,520,664, which is incorporated hereinby reference.

Chemotherapeutic agents can be coupled with the stent of the presentinvention in a manner analogous to that of antimicrobial agents.Exemplary chemotherapeutic agents include but are not limited tocis-platinum, paclitaxol, 5-flourouracial, gemcytobine and navelbine.The chemotherapeutic agents are generally grouped as DNA-interactiveagents, antimetabolites, tubulin-interactive agents, hormonal agents,hormone-related agents, and others such as asparaginase or hydroxyurea.Each of the groups of chemotherapeutic agents can be further divided bytype of activity or compound. The chemotherapeutic agents used incombination with the anti-cancer agents or benzimidazoles of thisinvention include members of all of these groups. For a detaileddiscussion of the chemotherapeutic agents and their method ofadministration, see Dorr, et al, Cancer Chemotherapy Handbook, 2dedition, pages 15-34, Appleton & Lange (Connecticut, 1994), hereinincorporated by reference.

Examples of DNA-Interactive agents include, but are not limited to,alkylating agents, DNA strand-breakage agents; intercalating andnonintercalating topoisomerase II inhibitors, and DNA minor groovebinders. Alkylating agents generally react with a nucleophilic atom in acellular constituent, such as an amino, carboxyl, phosphate, orsulfhydryl group in nucleic acids, proteins, amino acids, orglutathione. Examples of alkylating agents include, but are not limitedto, nitrogen mustards, such as chlorambucil, cyclophosphamide,isofamide, mechlorethamine, Melphalan, uracil mustard; aziridines, suchas thiotepa; methanesulfonate esters such as busulfan; nitroso, ureas,such as cannustine, lomustine, streptozocin; platinum complexes, such ascisplatin, carboplatin; bioreductive alkylator, such as mitomycin, andprocarbazine, dacarbazine and altretamine. DNA strand breaking agentsinclude, but are not limited to, bleomycin. Intercalating DNAtopoisomerase II inhibitors include, but are not limited to,intercalators such as amsacrine, dactinomycin, daunorubicin,doxorubicin, idarubicin, and mitoxantrone.

Nonintercalating DNA topoisomerase II inhibitors include, but are notlimited to etoposide and teniposide. DNA minor groove binders include,but are not limited to, plicamycin.

Antimetabolites interfere with the production of nucleic acids by one orthe other of two major mechanisms. Some of the drugs inhibit productionof the deoxyribonucleoside triphosphates that are immediate precursorsfor DNA synthesis, thus inhibiting DNA replication. Some of thecompounds, for example, purines or pyrimidines, are sufficient to beable to substitute for them in the anabolic nucleotide pathways. Theseanalogs can then be substituted into the DNA and RNA instead of theirnormal counterparts. The antimetabolites useful herein include: folateantagonists such as methotrexate and trimetrexate pyrimidineantagonists, such as fluorouracil, fluorodeoxyunridine, CB3717,azacytidine, cytarabine, and floxuridine purine antagonists includemercaptopurine, 6-thioguanine, fludarabine, pentostatin; sugar modifiedanalogs include cyctrabine, fludarabine; ribonucleotide reductaseinhibitors include hydroxyurea. Tubulin interactive agents act bybinding to specific sites on tubulin, a protein that polymerizes to formcellular microtubules. Microtubules are critical cell structure units.When the interactive agents bind on the protein, the cell cannot formmicrotubules tubulin interactive agents including vincristine andvinblastine, both alkaloids and paclitaxel.

Hormonal agents are also useful in the treatment of cancers and tumors.They are used in hormonally susceptible tumors and are usually derivedfrom natural sources. These include: estrogens, conjugated estrogens andethinyl estradiol and diethylstilbestrol, chlorotrianisene andidenestrol; progestins such as hydroxyprogesterone caproate,medroxyprogesterone, and megestrol; androgens such as testosterone,testosterone propionate; fluoxymesterone, methyltestosterone; adrenalcorticosteroids are derived from natural adrenal cortisol orhydrocortisone. They are used because of their anti-inflammatorybenefits as well as the ability of some to inhibit mitotic divisions andto halt DNA synthesis. These compounds include prednisone,dexamethasone, methylprednisolone, and prednisolone.

Hormone-related agents include, but are not limited to, leutinizinghormone releasing hormone agents, gonadotropin-releasing hormoneantagonists and anti-hormonal agents. Gonadotropin-releasing hormoneantagonists include leuprolide acetate and goserelin acetate. Theyprevent the biosynthesis of steroids in the testes and are usedprimarily for the treatment of prostate cancer.

Antihormonal agents include antiestrogenic agents such as tamoxifen,antiandrogen agents such as Flutamide; and antiadrenal agents such asmitotane and amminoglutethimide. Hydroxyurea appears to act primarilythrough inhibition of the enzyme ribonucleotide reductase. Asparaginaseis an enzyme that converts asparagine to nonfunctional aspartic acid andthus blocks protein synthesis in the tumor.

Gene transfer vectors are capable of introducing a polynucleotide into acell. The polynucleotide may contain the coding sequence of a protein ora peptide, or a nucleotide sequence that encodes a iRNA or antisenseRNA. Examples of gene transfer vectors include, but are not limited to,non-viral vectors and viral vectors. Non-viral vectors typically includea plasmid having a circular double stranded DNA into which additionalDNA segments can be introduced. The non-viral vector may be in the formof naked DNA, polycationic condensed DNA linked or unlinked toinactivated virus, ligand linked DNA, and liposome-DNA conjugates. Viralvectors include, but are not limited to, retrovirus, adenovirus,adeno-associated virus (AAV), herpesvirus, and alphavirus vectors. Theviral vectors can also be astrovirus, coronavirus, orthomyxovirus,papovavirus, paramyxovirus, parvovirus, picornavirus, poxvirus, ortogavirus vectors.

The non-viral and viral vectors also include one or more regulatorysequences operably linked to the polynucleotide being expressed. Anucleotide sequence is “operably linked” to another nucleotide sequenceif the two sequences are placed into a functional relationship. Forexample, a coding sequence is operably linked to a 5′ regulatorysequence if the 5′ regulatory sequence can initiate transcription of thecoding sequence in an in vitro transcription/translation system or in ahost cell. “Operably linked” does not require that the DNA sequencesbeing linked are contiguous to each other. Intervening sequences mayexist between two operably linked sequences.

In one embodiment, the gene transfer vector encodes a short interferingRNA (siRNA). siRNAs are dsRNAs having 19-25 nucleotides. siRNAs can beproduced endogenously by degradation of longer dsRNA molecules by anRNase III-related nuclease called Dicer. siRNAs can also be introducedinto a cell exogenously or by transcription of an expression construct.Once formed, the siRNAs assemble with protein components intoendoribonuclease-containing complexes known as RNA-induced silencingcomplexes (RISCs). An ATP-generated unwinding of the siRNA activates theRISCs, which in turn target the complementary mRNA transcript byWatson-Crick base-pairing, thereby cleaving and destroying the mRNA.Cleavage of the mRNA takes place near the middle of the region bound bythe siRNA strand. This sequence specific mRNA degradation results ingene silencing. In another embodiment, the gene transfer vector encodesan antisense RNA.

Examples of cells include, but are not limited to, stem cells or otherharvested cells.

Manufacture of Stent

The stent body and surface channels can be laser cut, water jet cut,extruded, stamped, molded, laythed or formed. In one embodiment, thestent is cut from a single polymer tube that may be extruded. The tubemay be hollow or the center may be cored out at varying diameterssuitable for the particular indication.

The stent is then etched and is formed on a suitable shaping device togive the stent the desired external geometry. Both the synthetic collartechniques and in vitro valuation techniques show the remarkable abilityof stents of the present invention to convert acting force intodeformation work absorbed by the angled structure, which preventsexcessive scaffolding stress, premature material fatigue and acceleratedobsolescence.

The stent of the present invention may be formed in such a way as toallow fluid flow to change in the pitch of the flow to improve flowdynamics and to speed the flow of fluids throughout the device. From atight radial design to a more longitudinal design.

In one embodiment, spiral surface channels with large cross-sectionareas are formed to accommodate large volumes of body fluid. In anotherembodiment, multiple channels with small cross-section area are formedto accommodate large volumes of body fluid. In another embodiment, thestent body contains a large center lumen to allow for fluid flow and aplurality of small cross-section area channels on the surface tostabilize the stent in vivo.

In another embodiment, the lips of the channel walls are taped toincrease the surface area for fluid flow and grip. Changes in the depthof the pitch of the channels will also have an impact on fluid flow andstability.

In one embodiment, the stent is formed on a shaping tool that hassubstantially the desired contour of the external stent dimensions. Inthe event the stent is to be shaped to the dimensions of a particularlumen, optical photography and/or optical videography of the targetlumen may be conducted prior to stent formation. The geometry ofcorresponding zones and connector regions of the stent then can beetched and formed in accordance with the requirements of that targetlumen. In particular, if the topography of the biliary duct of aparticular patient is captured optically and the appropriate dimensionprovided, a patient specific prosthesis can be engineered. Thesetechniques can be adapted to other non-vascular lumens but is very wellsuited for vascular applications where patient specific topography is afunction of a variety of factors such as genetics, lifestyle, etc.

Unlike stents made from shape memory metals, the stents of the presentinvention can take on an infinite number of characteristic combinationsas zones and segments within a zone can be modified by changing angles,segment lengths, segment thicknesses, pitch during the etching andforming stages of stent engineering or during post formation processingand polishing steps. Moreover, by modifying the geometry, depth, anddiameter of the channels between zones, additional functionality may beachieved such as flexibility, increased fluid transport, and changes infriction.

The above description is for the purpose of teaching the person ofordinary skill in the art how to practice the present invention, and itis not intended to detail all those obvious modifications and variationsof it which will become apparent to the skilled worker upon reading thedescription. It is intended, however, that all such obviousmodifications and variations be included within the scope of the presentinvention, which is defined by the following claims. The claims areintended to cover the claimed components and steps in any sequence whichis effective to meet the objectives there intended, unless the contextspecifically indicates the contrary.

1. A stent comprising: an elongated center rod having a proximate endand a distal end; and a plurality of leaflets extending outward fromsaid center rod and forming sinusoidal channels between two neighboringleaflets to provide fluid communication between said proximal end andsaid distal end, wherein said center rod and said leaflets comprise abioabsorable material.
 2. The stent of claim 1, wherein said pluralityof leaflets can be folded to reduce the diameter of said stent.
 3. Thestent of claim 2, wherein said plurality of leaflets can be foldedpivotally over each other.
 4. The stent of claim 1, wherein saidbioabsorable material is selected from the group consisting ofpolylactic acid or polylactide (PLA), polyglycolic acid andpolyglycolide (PGA), poly-epsilon-caprolactone (PCL),polyhydroxybutyrate (PHB) and co-polymers thereof.
 5. The stent of claim1, wherein said plurality of leaflets are contoured and aligned in a wayto increase the flow speed of a body fluid.
 6. The stent of claim 1,wherein said plurality of leaflets are connected to each other by anouter cam.
 7. The stent of claim 6, wherein said outer cam is beveled.8. The stent of claim 1, wherein said center rod comprises a centerlumen that allows said stent to slide into the place of implantationthrough a guide wire.
 9. The stent of claim 1, wherein said leaflets arethicker at base where said leaflets are attached to the rod.
 10. Thestent of claim 1, wherein said stent has a sinusoidal shape to conformto a body lumen.
 11. The stent of claim 1, wherein said stent isconstructed to allow unidirectional collapse of said leaflets byrotating said stent in one direction, wherein a collapsed stent isopenable by rotating said stent in a reversed direction.
 12. The stentof claim 11, wherein said stent has a diameter of 1 cm in openconfiguration and a diameter of 1 mm in folded configuration.
 13. Thestent of claim 1, wherein said leaflets are alternating in directions soas to prevent migration of an expanded stent.
 14. The stent of claim 1,wherein said stent has a tapered end.
 15. The stent of claim 1, whereinsaid bioabsorable material is embedded with an agent selected from thegroup consisting of small molecule drugs, biologicals and gene transfervectors.
 16. The stent of claim 1, wherein said bioabsorable material isembedded with an antiproliferating agent.
 17. The stent of claim 1,wherein said bioabsorable material is embedded with an antimicrobialagent or a chemotherapeutic agent.